1. Field of the Invention
This invention relates to a method of processing substrates and a substrate processing apparatus, utilized to produce semiconductor devices, such as a method of processing substrates and a substrate processing apparatus for forming films by the use of gas or the like or by means of ashing process, and more particularly to a batch type method of processing substrates and substrate processing apparatus.
2. Description of the Related Art
Semiconductor devices have been fabricated by means of thin film formation processes utilizing the vapor phase deposition method (the CVD method) due to vapor phase reactions, the epitaxial growth method and the like. Further, etching and ashing have been widely used. Particularly, the batch process which processes a plurality of substrates in one lot has frequently been used as a method having high productivity.
When the batch process is used, however, variation occurs in surface process of substrates. For example, in forming thin films on a plurality of substrates, the thickness and quality of the films vary. The variation occurs due to the fact that surface processing conditions are delicately changed according to the positions of the substrates arranged in a reaction vessel.
The reason why the variation occurs when thin films are formed will now be explained. In the CVD method and the epitaxial growth method, surface processing is carried out by a reaction caused by energy of heat, light, plasma or the like, decomposition of gas introduced in the reaction vessel, or a reaction of gas on the substrates. In the batch process, substrates are generally arranged in the direction of the flow of the gas introduced in the reaction vessel. The time interval of energy exposure to substrates at the upstream side of the gas flow is different from the time interval of energy exposure to substrates at the downstream side of the gas flow. Further, when a plurality of gases are mixed with each other in the reaction vessel, the mixed gas arrives at respective substrates at different time. In this connection, the degrees of the deposition or reaction of the gas (gaseous species) differ at different positions of the substrates. The process of CVD at lower temperatures is reported in J. Sato and K. Maeda: VERY LOW TEMPERATURE CVD OF SiO.sub.2 FILMS USING OZONE AND ORGANOSILANE (Electro Chemical Society, Spring Meeting, Abstract No. 9, pp. 31-33, May 1971).
As described above, the conventional batch process is encountered with a problem that the surface-processed states of substrates vary.